QDomNode::isNull() and QDomNode::hasChildNodes()

Bart_Vandewoestyne

While refactoring some code, I came across the following if-clause several times:

const QDomElement foo = mfGetSomeQDomElementFromSomewhere();
if (!foo.isNull() && foo.hasChildNodes())
{ ... do stuff ...}

I am wondering why the author added the check !foo.isNull()... I am thinking of refactoring this to

if (foo.hasChildNodes()) {...}

because if foo has child nodes, it implies that it is not null, right?

Just wanted to check my reasoning and that I haven't overlooked something. Feel free to confirm or point me to mistakes in my reasoning :-)

mrjj

Hi
Not checked with QDomElement but
such check can also be that
if foo.isNull() then its not safe to to call foo.hasChildNodes()
But purely speculating.

kshegunov

@Bart_Vandewoestyne said in QDomNode::isNull() and QDomNode::hasChildNodes():

because if foo has child nodes, it implies that it is not null, right?

Yes, but not having child nodes doesn't mean the node is null. ;)

Just wanted to check my reasoning and that I haven't overlooked something.

I don't think you have overlooked anything, it should be safe to remove the first part of the check.

Bart_Vandewoestyne

We are still using Qt 4.8.7, so I checked the source:

bool QDomNode::hasChildNodes() const
{
    if (!impl)
        return false;
    return IMPL->first != 0;
}

bool QDomNode::isNull() const
{
    return (impl == 0);
}

so from this I conclude that my assumption was right and the refactoring was ok :-)